1. Field of the Invention
This invention relates to metal air cells, and particularly to a metal air cells incorporating systems for extending the useful lifetime thereof.
2. Description of the Prior Art
Electrochemical power sources are devices through which electric energy can be produced by means of electrochemical reactions. These devices include metal air electrochemical cells such as zinc air and aluminum air batteries. Metal air electrochemical cells include an anode, a cathode, and an electrolyte for ionic communication between the anode and the cathode. The anode is generally formed of metal materials. The cathode generally comprises an air diffusion electrode for oxidizing air. The electrolyte is usually a caustic liquid that is ionic conducting but not electrically conducting.
Metal air electrochemical cells have numerous advantages over traditional hydrogen-based fuel cells. Metal air electrochemical cells have high energy density (W*hr/Liter) and high specific energy (W*hr/kg). Further, the supply of energy provided from metal air electrochemical cells is virtually inexhaustible because the fuel, such as zinc, is plentiful and can exist either as the metal or its oxide. Additionally, metal air cells are capable of operating at ambient temperatures. The fuel may be solid state, therefore, safe and easy to handle and store.
Metal air electrochemical cells operate at ambient temperature, whereas hydrogen-oxygen fuel cells typically operate at temperatures in the range of 150° C. to 1000° C. Metal air electrochemical cells are capable of delivering higher output voltages (1.5–3 Volts) than conventional fuel cells (<0.8V). Due to these advantages, metal air electrochemical cells can be used as power sources of all kind of applications, such as stationary or mobile power plant, electric vehicle or portable electronic device, etc.
One of the principle obstacles of metal air electrochemical cells is the prevention of electrochemical reaction during periods of non-use, or self-discharging. Such unwanted reaction leads to unnecessary use of metal fuel, degradation of the cathode, and drying of the electrolyte.
Therefore, a need remains in the art for a metal air cell that minimizes or preferably eliminates self-discharging.